April 17, 2012 AT 8:31 am

EE Bookshelf: The ‘Sound’ of Capacitors

Today’s bookshelf isn’t a datasheet or a book. It’s actually just a webpage (which I suppose would make it an ‘EE bookmark‘), but it’s one that I like a lot, so I figured I’d share it.

Which capacitors sound better than others? Or perhaps, which ones distort the least? This is a contentious topic among audiophiles, musicians, DIY synth builders and occasionally HAMs as well. I don’t actually want to wade into this argument. My main purpose in writing this post is to share with you this excellent webpage over at greygum.net. I keep this one near the top of my bookmarks folder, and make sure it stays there when I migrate to a new computer.

This page dates from 1999, but the information is still good. It’s also a great example of an awesome late-90’s webpage.

The author, Steve, performed some tests to find the D-E curve of various types of capacitors (his test set-up is described at the bottom of the page). The results can be eye-opening.

The two worst performers on that page were electrolytics (which exhibit marked hysteresis, particularly the tantalum, above), and ceramic monolithics, which have very noticeable distortion. The one thing both electrolytics and monolithics have in common is their relatively compact size, achieved in part by use of a very thin dielectric. It’s interesting to see that the high-voltage monolithic has less distortion than it’s low-voltage counterpart, perhaps in part because the HV version has a thicker and/or different dielectric.

While I had known from long-time experience that ceramic and electrolytic caps can muck up the signal path, I never had any data (visual or otherwise) to back it up — until I read about Steve’s experiment a few years ago. As such, I tend to relegate these caps to decoupling and bypassing, and use something else for anything that touches signal, usually polypropylene film.

1 Comment

I too, don’t want to wade into all of the psuedoscientific nonsense surrounding this topic, but I will say this-

If you are building some kind of audio gadget, and are looking for a specific sound, you most likely will be disappointed if you focus only on the capacitor type. You must also look at the rest of the circuit- at the very least, the stage where the cap is located. Other components will have a profound effect on the “contributions” made by any cap, magic or otherwise.

Of course, the best advice is to ignore anything that can’t be explained by scientific theory and sound engineering design practice, and of course, trust your ears. The human brain is very good at fooling itself, especially when it comes to buying into fashionable nonsense (The e
extraordinary popular delusions and the madness of crowds, if you will).

Learning a little about basic analog engineering and psycho-acoustics will get you much farther during your search for that special “sound.” That will put you miles ahead of the casual tinkerers who often come to well-intentioned, but erroneous conclusions due to their lack of knowledge of the basics.

Finally- with the ready availability of cheap DSP technology, almost any “sound” can be modelled with a good parametric equalizer (and perhaps a compressor) and a little skill.

"Do not train a child to learn by force or harshness; but direct them to it by what amuses their minds, so that you may be better able to discover with accuracy the peculiar bent of the genius of each" - Plato